1. Field of the Invention
The present invention relates to a method of assigning connection identifiers for virtual path connection (VPC) and virtual channel connection (VCC) in an asynchronous transfer mode (ATM).
2. Discussion of Related Art
Connection identifiers (VPI/VCI) are used to discriminate the connection between a subscriber and networks in an ATM switching system. Subscriber interfacing includes digital signal level 1 European (DS1E) supporting 2.048 Mbps, digital signal level 3 (DS3) supporting 44.736 Mbps, synchronous transport module 1 (STM1) supporting 155 Mbps, and STM4 supporting 622 Mbps.
According to the type of subscriber link connected in subscriber interface module (SIM), one subscriber link is interfaced in SIM for STM1, 3 for DS3, and 72 for DS1E. In ITU-T Q.2931 recommending interfacing between the subscriber and network for wideband service, the range of VPI for every subscriber interface is regulated to be within 0-255, the range of VCI inside the VP within 32-65535.
An existing N-ISDN switching system allows a limited number of channels inside the physical link between the subscriber and network. For instance, 2B+D interface has two channels transmitting user data so that only if they are discriminated is the subscriber data easily distinguished. Therefore, interfacing between subscriber and network is simply performed so that channel number allocation is managed only by indicating one being in use.
In B-ISDN switching system employing ATM, information for multiple connections is multiplexed because the broadband offered by one physical link is above 155 Mbps. Here, a connection identifier for discriminating user information is used, whose range is eight bits for VPI, and 16 bits for VCI.
In the ATM switching system, the range of connection identifiers available is wide so that it is almost impossible to indicate whether it is used or not, for every subscriber link. For this reason, contrary to the conventional method, the identifier cannot be limited to a predetermined range of values between subscriber and network when the subscriber link is installed.